Method of making semiconductor devices having protruding contacts

ABSTRACT

A method of making semiconductor devices with contacts protruding from openings in a passivation layer over an active chip area. Inside each opening, a relatively hard barrier layer is provided and a flash-plated film is applied to subsequently form a relatively soft diffusion barrier layer when a protruding contact is formed. Two semiconductor devices with electrodes are joined by embedding relatively hard electrodes of a first device into relatively soft electrodes of a second device. A reducing agent can be incorporated into an insulating resin applied between semiconductor chips at areas other than the bonded electrodes.

This is a Division of application Ser. No. 08/804,968 filed Feb. 24,1997 now U.S. Pat. No. 5,952,718.

TECHNICAL FIELD

The present invention is directed to semiconductor devices in general,and in particular to semiconductor devices having protruding contactsfor coupling those semiconductor devices with substrate electrodes ofother semiconductor devices or circuit boards. The present invention isalso directed to a method for manufacturing such semiconductor devices.

BACKGROUND ART

Known methods for coupling together two semiconductor devices or asemiconductor device and a circuit board include the tape automatedbonding (TAB) method, and flip chip method. The circuit board in thiscontext may include, in addition to printed circuit boards comprising aninsulating base board and an electro-conductive substrate electrode,thin film transistor (TFT) elements, piezoelectric elements and anyother electrical elements that may be coupled electrically withsemiconductor devices.

In the flip chip method, a semiconductor device to be mounted isprovided with protruding contacts of solder(e.g., a tin and lead alloy),and is coupled with another semiconductor device or circuit board bymeans of the protruding contacts.

FIG. 1 is a cross sectional view of a semiconductor device in which asemiconductor chip 11 comprises an active layer 16 containingtransistors, wirings, contacts, or the like, and a chip electrode 13.The chip electrode 13 is exposed via an opening formed in a protectionlayer 12 comprised of a low melting point glass, a silicon nitridelayer, or the like, covering the active surface 16 of semiconductor chip11. A barrier layer 14 comprised of TiW/Au, or the like, is formedinside and around the opening, and a protruding contact 15 is formed onthe barrier layer 14 by electrolytic plating or an evaporation process.The protruding contact 15 is connected to other semiconductor chips orcircuit boards.

FIG. 2 is another cross sectional view showing an exemplary combinationof semiconductor devices. A semiconductor chip 24 is provided with anAu-surfaced protruding contact 26 and the protruding contact 26 isconnected to a substrate electrode 27 made of Al formed on a circuitboard 25. An Au--Al alloy layer 28 is formed around the protrudingcontact 26 and the substrate electrode 27.

However, the conventional semiconductor device described with referenceto FIG. 1 has the following drawbacks. The barrier layer 14 is onceformed over the whole surface of the semiconductor wafer, and then theundesirable part is etched off, leaving protruding contacts 15. Thebarrier layer 14 thus has a shape that extends entirely around theopening to prevent overetching. Accordingly, the prior art process iscomplex. Furthermore, it is difficult in the above describedmanufacturing process to provide protruding contacts 15 at a fine pitch.This fact limits the possibility of manufacturing smaller semiconductordevices. In the case of a structure as shown in FIG. 1, the pitchbetween adjacent openings is approximately 20 μm (microns), the diameterof each opening is 100 μm and the height of each protruding contact is100 μm.

A conventional semiconductor device described with reference to FIG. 2has the following drawbacks. High temperature heating and heavy loadsare applied to semiconductor chip 24 while connecting semiconductor chip24 to the substrate electrode 27. Such temperatures and loads may leadto breakage and/or deteriorated reliability of semiconductor chip 24,resulting in a reduced manufacturing yield rate of the finished devices.

OBJECTIVE OF THE INVENTION

It is therefore an object of the present invention to providesemiconductor devices suitable for miniaturization, as well as a methodfor manufacturing such semiconductor devices.

Another object of the present invention is to provide semiconductordevices having strong resistivity against mechanical stress, as well asa method for manufacturing such semiconductor devices.

SUMMARY OF THE INVENTION

Semiconductor devices in accordance with the present invention comprisea protection layer which covers the active surface of a semiconductorchip and is provided with openings corresponding to chip electrodesdisposed on the active surface of the semiconductor chip. Providedinside the opening are a barrier layer for covering the chip electrode,a diffusion barrier layer covering the barrier layer and a protrudingcontact provided on the diffusion barrier layer.

The aggregated layer thickness of the barrier layer and the diffusionbarrier layer should preferably be approximately equal to that of theprotection layer.

Further, the hardness of the protruding contact should preferably belower than that of the chip electrode and barrier layer.

Semiconductor devices in accordance with the present invention comprisea first semiconductor device having a first protruding contact and asecond semiconductor device or a circuit board having a secondprotruding contact whose hardness is lower than that of the firstprotruding contact of the first semiconductor device. The semiconductordevice is formed with a structure in which the first protruding contactis embedded in the second protruding contact.

Advantageously, the first and the second semiconductor devices areprovided with a protection layer which covers the active surface of thesemiconductor chip and has openings corresponding to the chip electrodesdisposed on the active surface of the semiconductor chip. Providedinside the openings are a barrier layer for covering the chip electrodeand a diffusion barrier layer covering the barrier layer.

The first protruding contact should preferably be comprised of one ofgold, palladium, platinum, copper and alloys containing these elementsas the principal ingredient. For example, an alloy copper as theprincipal ingredient would comprise 80% copper and 20% nickel. Thesecond protruding contact should preferably be comprised of one ofindium, lead and alloys containing these elements as the principalingredient. For example, an alloy comprising indium as the principalingredient would comprise 90% indium and 10% gold.

Semiconductor devices in accordance with the present invention comprisea first and a second semiconductor device, each of which is providedwith a protection layer which covers the active surface of thesemiconductor chip and is provided with openings corresponding to thechip electrodes disposed on the active surface of the semiconductorchip. Provided inside the openings are a barrier layer for covering thechip electrode and a diffusion barrier layer covering the barrier layer.On the diffusion barrier layer is a protruding contact whose hardness islower than that of the chip electrode and the barrier layer.

The gap between the first and the second semiconductor devices shouldpreferably be filled with an insulating resin.

Further, the insulating resin should preferably be a thermosettinginsulating resin containing a reducing agent.

Furthermore, the mixing ratio of the reduction agent to the insulatingresin should preferably be 40-80 volume %.

A method for manufacturing the semiconductor devices according to thepresent invention comprises the steps of forming by electroless platinga barrier layer and a film for forming a diffusion barrier layer on achip electrode which is exposed through an opening in the protectionlayer covering the active surface of the semiconductor chip; and forminga protruding contact on the film for forming a diffusion barrier layer,and a diffusion barrier layer by the mutual diffusion of the protrudingcontact and the film for forming a diffusion barrier layer.

A method for manufacturing semiconductor devices according to thepresent invention comprises the steps of aligning a protruding contactformed on a first semiconductor device with the film for forming adiffusion barrier layer on a second semiconductor device or a circuitboard; forming a diffusion barrier layer by the mutual diffusion of theprotruding contact and the film for forming a diffusion barrier layer;and connecting together the first semiconductor device and the secondsemiconductor device or a circuit board.

A method for manufacturing semiconductor devices according to thepresent invention comprises the steps of forming a first and a secondprotruding contact, each having different hardnesses; aligning the firstand the second protruding contacts together; and embedding, at least apart of, the protruding contact of higher hardness in the otherprotruding contact.

A method for manufacturing semiconductor devices according to thepresent invention comprises the steps of forming a first and a secondprotruding contact having different hardnesses on a first semiconductorchip and a second semiconductor chip or a circuit board; aligning thefirst and the second protruding contacts together and embedding, atleast a part of, a protruding contact of higher hardness in the otherprotruding contact; and applying an insulating resin around the firstand the second protruding contacts.

A method for manufacturing semiconductor devices according to thepresent invention comprises the steps of forming first and secondprotruding contacts having different hardnesses on a first semiconductorchip and a second semiconductor chip or a circuit board; aligning theprotruding contacts with each other; applying an insulating resin aroundthe first and the second protruding contacts and pressing the first andthe second semiconductor chips together; and hardening the insulatingresin.

A method for manufacturing semiconductor devices according to thepresent invention comprises the steps of aligning a protruding contacton a first semiconductor device with an electrode on a secondsemiconductor device or a circuit board; applying an insulating resincontaining a reducing agent to a protruding contact on the firstsemiconductor device and/or an electrode of the second semiconductordevice or the circuit board; and hardening the insulating resin.

A method for manufacturing semiconductor devices in accordance with thepresent invention comprises the steps of forming first and secondprotruding contacts having different hardnesses respectively on a firstsemiconductor chip and a second semiconductor chip or a circuit board;aligning said first protruding contact with said second protrudingcontact; applying an insulating resin containing a reducing agent aroundsaid first and/or second protruding contact; connecting said first andsecond protruding contacts together such that at least a part of theprotruding contact of higher hardness is embedded in the otherprotruding contact; and hardening said insulating resin.

Semiconductor devices in accordance with the present invention comprisea first semiconductor device and a second semiconductor device or acircuit board the electrodes of which are electrically connected to eachother, and an insulating resin containing a reducing agent which fills agap between the first semiconductor device and the second semiconductordevice or circuit board.

Still other objects and advantages of the present invention will becomereadily apparent to those skilled in this art from the followingdetailed description, wherein we have shown and described only thepreferred embodiment of the invention, simply by way of illustration ofthe best mode contemplated by us of carrying out our invention. As willbe realized, the invention is capable of other and differentembodiments, and its several details are capable of modifications invarious obvious respects, all without departing from the invention.Accordingly, the drawing and description are to be regarded asillustrative in nature, and not as restrictive.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross sectional view of a prior art semiconductor device.

FIG. 2 is a cross sectional view of another prior art semiconductordevice.

FIG. 3 is a cross sectional view of a semiconductor device according toan embodiment of the present invention.

FIG. 4 is shows a process step for manufacturing a semiconductor deviceaccording to an embodiment of the present invention.

FIGS. 5a-5c show a process for transferring a protruding contact onto asemiconductor device according to the present invention.

FIG. 6 is a cross sectional view of an exemplary combination of theinventive semiconductor devices according to an embodiment of thepresent invention.

FIG. 7 shows a process for connecting two semiconductor devicesaccording to an embodiment of the present invention.

FIG. 8 is a cross sectional view of an exemplary combination of twosemiconductor devices according to an embodiment of the presentinvention.

FIGS. 9 through 13 each show a process step for connecting twosemiconductor devices according to an embodiment of the presentinvention.

FIGS. 14 through 17 each show a process step for connecting twosemiconductor devices according to another embodiment of the presentinvention.

FIG. 18 is a cross sectional view of an exemplary connection of asemiconductor device and a circuit board according to an embodiment ofthe present invention.

FIGS. 19a-19b show a process for connecting a semiconductor device and acircuit board according to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

FIG. 3 shows a cross sectional view of a semiconductor device accordingto a preferred embodiment of the present invention. Provided inside asemiconductor chip 31 is an active layer 32 comprising transistors,wirings, contacts, or like structures. On the active surface ofsemiconductor chip 31, chip electrodes 33 such as Al electrodes areformed at intervals of approximately 30 μm. The chip electrode of thepresent embodiment comprises an Al material, containing about 0.5% Cu,having a thickness of approximately 0.6 μm. The main material for chipelectrode 31, however, is not limited to Al, but the chip electrode maycomprise a material containing Cu as the principal ingredient.

Formed on the active surface of semiconductor chip 31 is a protectionlayer 34, which is a silicon nitride film approximately 0.8 μm thick.The protection layer 34 is provided with openings each having a 15 μminner diameter disposed at appropriate intervals for exposing the chipelectrodes 33 of semiconductor chip 31. The protection layer 34 may alsocomprise a low melting point glass. Inside each opening, a layer ofplated Ni approximately 0.3 μm thick covers the chip electrode 33 as abarrier layer 35. Further, a diffusion barrier layer 36 approximately0.5 μm thick covers the barrier layer 35. On the diffusion barrier layer36, protruding contact 37, approximately 10 μm high, is provided.

In the present preferred embodiment, the aggregated thickness of barrierlayer 35 and diffusion barrier layer 36 is approximately equal to thethickness of protection layer 34. The barrier layer 35 and diffusionbarrier layer 36 should be formed to cover the inside of the opening.The aggregated thickness of barrier layer 35 and diffusion barrier layer36 may be less than the thickness of protection layer 34. However, it ispreferable that the aggregated thickness of barrier layer 35 anddiffusion barrier layer 36 be almost identical to the thickness ofprotection layer 34 thereby creating a stable coupling state whenmounting a semiconductor device on a circuit board or connectingsemiconductor devices together. Furthermore, it is preferred that thebarrier layer 35, diffusion barrier layer 36 and protruding contact 37each have essentially the same diameter as the inner diameter of theopening.

The protruding contact 37 comprises material such as In, or the like,whose hardness is lower than Al and Ni. By using In, for example, theprotruding contact absorbs mechanical stress that is typicallytransmitted to the active layer through the barrier layer and chipelectrode when a semiconductor device is pressed against anotherelectrode.

The above-described mechanical stress transmission phenomenon isdescribed in more detail below. Since the Vickers hardness of Ni, forexample, is about 450-500 Hv, and that of In is about 1-4 Hv, theprotruding contact 37 of In experiences plastic deformation therebyalleviating the mechanical stress that would normally be transmitted toactive layer 32 through barrier layer 35 and chip electrode 33.

The diffusion barrier layer 36 is formed by the following process steps.On the barrier layer 35 comprised of plated Ni film, a film for forminga diffusion barrier layer 38 is formed by flash plating Au until it isapproximately 0.1 μm thick, as shown in FIG. 4. The Vickers hardness ofAu is approximately 30-40 Hv. When a protruding contact 37 comprised ofIn contacts the film for forming a diffusion barrier layer 38, aninter-metallic compound of AuIn₂ as thick as approximately 0.5 μm isformed through the mutual diffusion of Au and In. The resulting layerbecomes a diffusion barrier layer 36.

The diffusion barrier layer 36 prevents the mutual diffusion of Ni andIn and, at the same time, also assures the secure adhesion of barrierlayer 35 and protruding contact 37. The material comprising theprotruding contact is not limited to In only, but may also includematerials whose hardness is lower than that of chip electrode 33 andbarrier layer 36. One example of another suitable material is lead.Furthermore, the material comprising the film for forming diffusionbarrier layer 38 is not limited to Au only, but may also include Pd oran In/Pb alloy.

As described above, in a semiconductor device according to a preferredembodiment of the present invention, the barrier layer 35 and thediffusion barrier layer 36 are formed only inside the opening ofprotection layer 34, and the protruding contact 37 is formed on barrierlayer 35 via diffusion barrier layer 36. Such a configuration makes itunnecessary to etch a barrier layer that extends beyond the opening.Thus, the size of protruding contact 37 itself, as well as the spacingbetween the protruding contacts, may be made smaller. In a case of thepresent embodiment, it is possible to reduce the diameter of the openingto as small as 15 μm, and the distance between adjacent openings toapproximately 30 μm. As the hardness of protruding contact 37 is lowerthan that of chip electrode 33 and barrier layer 35, mechanical stresswhich may arise when a semiconductor device is mounted, for example, ona circuit board, is absorbed by protruding contact 37, and thepossibility of mechanical stress reaching the active layer 32 isdiminished.

A method for manufacturing such semiconductor devices will be describednext with reference to FIG. 4. Spaced apart chip electrodes 33 comprisedof Al, or the like, are formed by sputtering on the active surface 32 ofsemiconductor chip 31. A protection layer 34 of silicon nitride film isformed by CVD on the active surface 32 of semiconductor chip 31. Then,openings are provided in the protection layer 34 at locationscorresponding to the spaced apart chip electrodes 33 thus exposing thechip electrodes 33. On the chip electrode 33 exposed through theopening, a Ni film is formed by electroless plating, which filmfunctions as a barrier layer 35. On the barrier layer 35, an Au flashfilm is formed by electroless plating. The Au film is used for forming adiffusion barrier layer 38 for providing a diffusion barrier layer 36.Then, on the film for forming a diffusion barrier layer 38, a protrudingcontact 37 of In is formed.

A process for transcribing or transferring the protruding contacts 37 ofIn onto a semiconductor chip will be described next with reference toFIGS. 5a-5c.

A first semiconductor chip 31 is held by a pressing tool 40, as shown inFIG. 5a. Provided on the semiconductor chip 31, are both a Ni platedfilm, which functions as barrier layer 35, and an Au flash plated filmcovering barrier layer 35 which functions as a film for forming adiffusion barrier layer 38. Meanwhile, a piece of In 52 is attached, by,for example, electrolytic plating, to an indium tin oxide (ITO)substrate 51 formed on a SiO₂ substrate 50. A reducing agent 53 isapplied on the ITO substrate 51 covering the In piece 52. After the Inpiece 52 is aligned with the film for forming a diffusion barrier layer38, the semiconductor chip 31 is pressed towards SiO₂ substrate 50 bypressing tool 40. As the adhesion strength between In piece 52 and ITOsubstrate 51 is not very high, In piece 52 is easily transferred ontosemiconductor chip 31. Furthermore, since the hardness of In isrelatively low, the piece deforms as shown in FIG. 5b. A part of thereduction agent 53 is also transferred to semiconductor chip 31.

The In piece 52 thus transferred is heated by pressing tool 40,resulting in hemispheric shape, as shown in FIG. 5c, thus providing aprotruding contact 37. Diffusion barrier layer 36 is formed through themutual diffusion of the film for forming a diffusion barrier layer 38and the In piece 52. During this time, the film for a diffusion barrierlayer 38 does not diffuse over the whole In piece 52. Therefore, thehardness of protruding contact 37 remains almost identical to that of Initself. As a result, although the height of protruding contact 37 islow, the deforming properties of the protruding contact 37 are notaffected.

By transcribing the In piece 52 onto semiconductor chip 31 with reducingagent 53 applied in advance, oxidized materials existing between the Inpiece 52 and the Au flash plated layer, which functions as the film forforming a diffusion barrier layer 38, are removed, thereby resulting inimproved connection reliability between the In piece 52 and the Au flashplated layer. Furthermore, as oxidized materials covering the surface ofthe protruding contact are more significantly removed as compared withthe case where no reduction agent is applied, the reliability ofconnection between, for example, the protruding contact 37 and anotherelectrode is improved.

Two semiconductor devices each having a structure as illustrated in FIG.3 may also be connected together. By so doing, the size of the coupleddevice is more compact compared to a single semiconductor device havingthe same function. Accordingly, the coupled device requires less areafor mounting. When connecting two semiconductor devices, each of thesemiconductor devices mutually receives an external pressing forceresulting in mechanical stress. That pressing force is typicallytransmitted to the active surface 32 of semiconductor chip 31 via chipelectrode 33 and barrier layer 35. In semiconductor devices of thepresent invention where the diameter of an opening is as small asapproximately 15 μm, it is feared that the pressure per unit areaapplied to the active surface 32 will be greater than that in aconventional semiconductor device, and, therefore, the device might beseriously affected by the mechanical stress.

FIG. 6 illustrates a structure for connecting semiconductor devices inwhich the above described problem is solved. Each semiconductor deviceshown in FIG. 6 has an individual structure identical to that of thesemiconductor device shown in FIG. 3. A detailed description thereofwill therefore be omitted. For convenience, the same numeraldesignations are used for those components having the same function asin FIG. 3.

In a combination of semiconductor devices as illustrated in FIG. 6, twosemiconductor devices are connected together at the protruding contacts37. A gap between the respective protection layers 34 is filled with aninsulating resin 39.

In the above described combination of semiconductor devices, each of thesemiconductor devices comprises an opening formed in the protectionlayer 34, a barrier layer 35 and a diffusion barrier layer 36 eachprovided inside the opening. The semiconductor devices are connectedtogether by joining respective protruding contacts 37 the hardness ofwhich is lower than that of chip electrode 33 and barrier layer 35.

The semiconductor devices of the above described combination aremanufactured by the following process steps. First two semiconductordevices as shown in FIG. 3 are prepared. The protruding contacts 37 ofone semiconductor device are aligned with those of the othersemiconductor device, and a specified quantity of an insulating resin39, e.g., epoxy resin, is applied on protection layer 34 of at least oneof the semiconductor devices. Then, one of the semiconductor devices ispressed against the other semiconductor device, and heated. Theprotruding contacts 37 are thus mutually affixed and the insulatingresin 39 is hardened. Through the above process steps, the protrudingcontacts 37 suffer a plastic deformation, thereby alleviating isexternal pressure that would normally be conveyed to the active layer 32via barrier layer 35 and chip electrode 33. Warpage of each respectivesemiconductor device and any excess height of any of protruding contacts37 are also absorbed by the above process.

In the present embodiment, one of the two semiconductor devices may bereplaced with a circuit board. In this case, an electrode on the circuitboard and a semiconductor device are connected by means of a protrudingcontact formed on the semiconductor device.

FIG. 7 shows another method for manufacturing semiconductor devices of adifferent combination. In the embodiment shown in FIG. 7, asemiconductor device as shown in FIG. 3 (x device) and asub-semiconductor device (y device), namely a semiconductor deviceaccording to FIG. 3 with diffusion barrier layer 36 and protrudingcontact 37 eliminated therefrom, are prepared. The sub-semiconductordevice y is provided with a film for forming a diffusion barrier layer38 on the barrier layer 35. Protruding contacts 37 of semiconductordevice x are aligned with the film for forming a diffusion barrier layer38 of sub-semiconductor device y. Then, an insulating resin 39 isapplied on protection layer 34 of at least one of the semiconductordevice x and sub-semiconductor device y. In the present embodiment, theinsulating resin 39 is applied on protection layer 34 ofsub-semiconductor device y.

At least one of the semiconductor device x and sub-semiconductor devicey is then pressed against the other and heated. As a result, the filmfor forming a diffusion barrier layer 38 or sub-semiconductor device yand the protruding contacts 37 of semiconductor device x mutuallydiffuse to form a diffusion barrier layer 36 of an increased thicknesson barrier layer 35 of sub-semiconductor device y. Thus, thesemiconductor device x and the sub-semiconductor device y are attachedtogether by means of protruding contact 37, and the insulating resin 39is hardened to further strengthen the bond between semiconductor devicex and sub-semiconductor device y, thereby resulting in a single-bodydevice.

In place of the sub-semiconductor device y, other electric deviceshaving electrodes provided with a film for forming a diffusion barrierlayer 38 such as a circuit board, may be used in the above embodiment.

Next, yet another structure for combining semiconductor devicesaccording to another embodiment will be described.

For convenience, only a semiconductor chip 31, a chip electrode 33 andprotruding contacts 37 are shown in FIG. 8 as the constituents of thesemiconductor device. However, a semiconductor device as illustrated inFIG. 3 may also be used.

On the surface of a first semiconductor chip 31a a first protrudingcontact 37a is provided, while on the surface of a second semiconductorchip 31b a second protruding contact 37b is provided. The firstprotruding contact 37a and the second protruding contact 37b areelectrically coupled together. A gap between the first semiconductorchip 31a and the second semiconductor chip 31b is filled with aninsulating resin 39. The hardness of the second protruding contact 37bis lower than that of the first protruding contact 37a. Also, the secondprotruding contact 37b should preferably be formed over a relativelylarger area.

Preferably, the first protruding contact 37a comprises Ni with an Aulayer, while the second protruding contact 37b comprises Ni with an Aulayer plus an In covering. The Vickers hardness of In is as low asapproximately 1-4 Hv. Thus, when the first protruding contact 37a andthe second protruding contact 37b are mated together, at least a part,e.g. a tip of the first protruding contact 37a, embeds into the secondprotruding contact 37b. An appropriate hardness level of the secondprotruding contact 37b is around 1-20 Hv in Vickers hardness foraccepting the first protruding contact 37a. Therefore, besides In, analloy in which In is the principal ingredient, Pb and an alloy in whichPb is the principal ingredient are also all suitable for the secondprotruding contact 37b. Suitable materials for the first protrudingcontact 37a include Au, Pd, Pt, Cu and alloys in which these elementsare the principal ingredients.

A method for manufacturing semiconductor devices of the abovecombination will be described next.

FIG. 9 is a side view showing how the first protruding contacts 37a arealigned with the second protruding contacts 37b. In the presentembodiment, the first protruding contacts 37a are each shaped on anelectrode 5-20 μm in diameter by providing, by electroless plating, Nito a thickness of 3-5 μm and Au to a thickness of 0.2-2 μm. The secondprotruding contacts 37b are each shaped on an electrode 20-100 μm indiameter by providing, by electroless plating, Ni to a thickness of 2 μmand Au to a thickness of 0.2 μm, and then In to a thickness of 3-5 μm bytranscription or by dipping. A pressing tool 40 comprising a vacuumdevice (not shown) picks up the first semiconductor chip 31a. Thepressing tool 40 maintains the vacuum and moves the first semiconductorchip 31a such that the first protruding contacts 37a are aligned withthe second protruding contacts 37b.

FIG. 10 is a side view showing a process for connecting the first andthe second protruding contacts, 37a and 37b. Using the pressing tool 40,the first protruding contacts 37a and/or the second protruding contacts37b are pressed with a load of less than 5 g per each protruded contact,and are thereby connected. The Vickers hardness of In, being a principalingredient of the second protruding contact 37b, is as low asapproximately 1-4 Hv, whereas that of Ni and Au, which constitute thefirst protruding contact 37a, is as high as 450-500 Hv and 40-50 Hv,respectively. Therefore, at least a part, e.g. a tip, of the firstprotruding contacts 37a are easily embedded into the second protrudingcontacts 37b, and electrical contact is established. The firstprotruding contacts 37a should preferably be embedded into the secondprotruded contacts 37b by about 2-4 μm.

FIG. 11 is a side view showing a process for filling a gap between afirst semiconductor chip 31a and a second semiconductor chip 31b with aninsulating resin 39. In the process, the insulating resin 39 is filledby taking advantage of the capillary phenomenon between the firstsemiconductor chip 31a and the second semiconductor chip 31b.

FIG. 12 is a side view showing a process for hardening an insulatingresin 39. Ultraviolet rays are irradiated by a UV lamp, preferably froman oblique angle with respect to the coupled first and secondsemiconductor chips, 31a and 31b.

FIG. 13 is a side view showing a process for withdrawing the pressingtool 40 and ultraviolet irradiation UV lamp 41. When the pressing andthe UV irradiation are withdrawn, a combination of two semiconductorchips is completed as shown in FIG. 8.

According to the preferred embodiments, since the area of each of thesecond protruding contacts 37b is larger than that of the firstprotruding contacts 37a and the hardness of the former is lower, the tipof the first protruding contacts 37a are easily embedded into the secondprotruding contacts 37b, enabling connection at low temperature and lowload. As a result, the risk of deteriorated semiconductor chipsresulting from the conventional connection process of two semiconductorchips, which includes high temperatures and high loads, is alleviated.Thus, according to the present invention it is possible to providecoupled semiconductor devices of high reliability. Furthermore, sincethe first protruding contacts 37a are connected by embedding the sameinto the second protruding contacts 37b, a reliable connection isassured.

Next, a method for manufacturing semiconductor devices of yet a furtherdifferent combination is described. In the present embodiment, firstprotruding contacts 37a comprise Ni, while a second protruding contacts37b comprise Ni and Au on top of which is added an In--Sn alloycomprising, for example, 90% In and 10% Sn.

More particularly, the first protruding contacts 37a are formed byplating Ni, by electroless plating, to a thickness of about 3 μm; thesecond protruding contacts 37b are formed by plating, by electrolessplating, Ni to a thickness of about 1 μm and Au to a thickness of about0.2 μm and provided by transcription or dipping over those layers anIn-Sn alloy about 3-5 μm thick. The diameter of each of the firstprotruding contacts 37a is 5-20 μm, and that of each of the secondprotruding contacts 37b is 20-100 μm. The structure of the rest of thedevice is the same as that shown in FIG. 11.

As shown in FIG. 14, the protruding contacts 37a and 37b of the firstsemiconductor chip 31a and the second semiconductor chip 31b,respectively, are made to engage each other by use of pressing tool 40.FIG. 15 is a side view showing how an insulating resin 39 curable byultraviolet rays is applied on at least one of the first and the secondsemiconductor chips. In the present case, the resin 39 is applied on thesecond semiconductor chip 31b. Namely, according to the present process,an insulating resin 39 is applied on at least one of the semiconductorchips before the first semiconductor chip 31a and the secondsemiconductor chip 31b are coupled together. FIG. 16 is a side viewshowing how the first protruding contacts 37a and the second protrudingcontacts 37b are connected, and the ultraviolet rays are irradiated.Namely, the first and second protruding contacts are pressed together bypressing tool 40 with a load of less than 5 g per each protrudingcontact, and the tips of the first protruding contacts 37a are embeddedinto the second protruding contacts 37b by approximately 2 μm. And then,the insulating resin 39 is hardened by UV irradiation from ultravioletray lamp 41. FIG. 17 is a side view showing how the pressing tool 40 andthe ultraviolet ray lamp 41 are withdrawn. Through the above describedprocess, the first semiconductor chip 31a and the second semiconductorchip 31b are mutually connected together.

According to the present preferred embodiment, the insulating resin 39is applied before the first protruding contacts 37a and the secondprotruding contacts 37b are connected together, and then hardened by theUV irradiation. It is therefore relatively easy to place an insulatingresin 39 between the first semiconductor chip 31a and the secondsemiconductor chip 31b.

In a combination where two semiconductor chips are stacked, it ispreferable to remove with a reducing agent, in advance, the oxidizedmaterials covering the surface of a protruding contact 37. An example ofsuch a reducing agent includes a reducing agent containing abietic acidas the principal ingredient. For example, a compound comprising morethan 80% abietic acid would be suitable.

The reducing agent used for removing oxidized materials needs to bewashed off or evaporated by heat after the coupling process is finished.However, it was found that the mounting efficiency in semiconductordevices coupled together in accordance with the present invention waslow since it took a relatively long time to completely discharge or washoff the reducing agent, because the height and/or pitch of theprotruding contacts are smaller in coupled semiconductor devices of thepresent invention.

The above described drawback of the present invention may be overcome byusing an insulating resin containing a reducing agent as the insulatingresin in connecting two semiconductor devices.

FIG. 18 is a side view showing how a semiconductor device of theinvention, e.g. FIG. 3, is mounted on a circuit board 25 by a face-downbonding method. In the present case, protruding contacts 37 comprise alow melting point metal such as a Sn--Pb solder, having a height lowerthan 10 μm, formed on chip electrode 33 by electrolytic plating,evaporation or any other appropriate method. The circuit board 25comprises a glass ceramic substrate, or the like, and substrateelectrodes 27 formed on the surface thereof. In the present case, thesubstrate electrodes 27 comprise a metal film of Cu and Ni, covered bySn--Pb solder several microns thick.

A gap between a protection layer 34 of semiconductor device 31 and thecircuit board 25 is filled with an insulating resin 39. The insulatingresin 39 comprises a thermosetting resin like epoxy resin having aviscosity of approximately 1500 c.p.s. containing a reducing agent 42for removing oxidized materials such as a reducing agent in whichabietic acid is the principal ingredient. The protruding contacts 37 andthe substrate electrodes 27 are electrically coupled together. Thereducing agent 42 is crushed between the protruding contacts 37 and thesubstrate electrodes 27, and oxidized materials covering the surface ofprotruding contacts 37 or substrate electrodes 27 are removed as aresult of the crushing and dispersing of reducing agent 42.

The reducing agent 42 is provided by spraying a wash-free type reducingagent in an active atmosphere maintained at a temperature ofapproximately 200° C., and rapidly cooling the reducing agent therebyhardening at least the surface thereof to yield a desired shape. Or, thereducing agent 42 may be a chunk-shaped reducing agent with its surfacecoated with an insulating resin such as epoxy resin or a thermoplasticresin such as polyamide, or a powdered or liquidized reducing agentsealed into a capsule made of an insulating resin or a thermoplasticresin. If the surface of reducing agent 42 is coated with an insulatingresin having the same properties as the insulating resin 39, or thereducing agent 42 is sealed in a capsule having the same properties asthe insulating resin 39, adhesion between the reducing agent 42 and theinsulating resin 39 is increased, thereby reducing the necessarypressure when mounting a semiconductor device on a circuit board.

The mixture ratio of the reducing agent 42 in the insulating resin 39 iswithin a range of 40-80 in volume %. Within that range, the reducingagent 42 exists to a very high probability between the protrudingcontact 37 and its counterpart substrate electrodes 27. In the case whenthe mixture ratio is lower than 40 volume %, the quantity of reducingagent 42 is too small to completely remove oxidized materials. On theother hand, if the mixture ratio exceeds 80 volume % the protectiveeffect of the insulating resin 39 may not be sufficient.

FIGS. 19a and 19b are side views showing a process wherein asemiconductor device is mounted on a circuit board. As shown in FIG.19a, a semiconductor chip 31 and a circuit board 25 are disposed face toface, and protruding contacts 37 and substrate electrodes 27 arealigned. A thermosetting insulating resin 39 which contains a reducingagent 42 having a chunk shape, or the like, is applied on the circuitboard 25 by dripping or other like method. And then, as shown in FIG.19b, the semiconductor chip 31 is pressed against the circuit board 25,and the protruding contacts 37 contact the substrate electrodes 27.Reducing agent 42 contained in insulating resin 39 is held between theprotruding contacts 37 and the substrate electrodes 27 and is crushedbetween the two. The reducing agent thus crushed disperses over each ofthe surfaces of protruding contacts 37 and substrate electrodes 27, andremoves oxidized materials therefrom.

By heating the semiconductor chip 31 with protruding contacts 37 andsubstrate electrodes 27 contacting each other, the protruding contacts37 and the substrate electrodes 27 are connected both physically andelectrically by metal diffusion. The insulating resin 39 applied betweenprotruding contacts 37 and substrate electrodes 27 are hardened at thesame time. Although in the above described manufacturing process thesemiconductor chip 31 is heated while being pressed, it is not essentialto maintain the pressing force if the viscosity or the adhesionproperties of insulating resin 39 is sufficiently high.

Heating may be applied, not to the semiconductor chip 31 alone, but alsoat the same time to both semiconductor chip 31 and circuit board 25. Thereducing agent 42 mixed with the insulating resin 39 need notnecessarily have a chunk shape. It may be mixed as a powder state orliquid contained in a capsule made from an insulating resin or athermoplastic resin.

In a conventional process, the insulating resin is applied after thereducing agent provided on the surface of circuit board was washed offor volatilized. According to the above described preferred embodiment,however, the process for washing off or volatilizing the reducing agentis eliminated. As a result, there is no mechanical stress exerted on theprotruding contacts due to washing, and there is no need to provide aclearance for discharging the volatilized substance. This isparticularly advantageous for miniaturized semiconductor devices.

The invention may be also embodied in other specific forms withoutdeparting from the spirit or essential characteristics thereof.

As described in the foregoing, semiconductor devices according to thepresent invention comprise a barrier layer and a diffusion barrier layerformed only over an area confined by an opening in the protection layer.As a result, it is possible to make the size and the pitch of protrudingcontacts smaller. Further, because the hardness of the protrudingcontacts is preferably lower than that of the chip electrode and barrierlayer, the risk of damage due to mechanical stress arising when asemiconductor device is mounted on a circuit board, and which wouldnormally be transmitted to the active layer of a semiconductor chip, isalleviated.

In a structure where two semiconductor devices are combined, each of theprotruding contacts of one device has a hardness different from that ofeach of the protruding contacts of the other device, such that one maybe embedded into the other. Therefore, the risk of damage due tomechanical stress being transmitted to the active layer of semiconductorchip is alleviated.

Furthermore, when an insulating resin, used when coupling together twosemiconductor devices or mounting a semiconductor device on a circuitboard, contains a reducing agent, it is possible to obtain a combinationof semiconductor devices in which neither washing the reduction agentnor discharging the volatilized reduction agent is needed.

What is claimed:
 1. A method for manufacturing a semiconductor device,comprising the steps of:forming, by electroless plating, a barrier layerand a flash-plated film for forming a diffusion barrier layer on a chipelectrode exposed through an opening in a protection layer covering anactive layer of a semiconductor chip; and forming a protruding contacton said film for forming a diffusion barrier layer, and forming adiffusion barrier layer, that is softer than the barrier layer, bymutual diffusion of said protruding contact and said film for forming adiffusion barrier layer.
 2. A method for manufacturing a semiconductordevice, comprising the steps of:providing a first semiconductor devicehaving a protruding contact formed thereon; providing at least one of acircuit board and a second semiconductor device, having thereon aflash-plated film for forming a diffusion barrier layer; abutting saidprotruding contact with said film for forming a diffusion barrier layer;forming a diffusion barrier layer, that is softer than the barrierlayer, by mutual diffusion of said protruding contact and said film forforming a diffusion barrier layer; and electrically coupling said firstsemiconductor device and said second semiconductor device by saidprotruding contact.
 3. A method for manufacturing a semiconductordevice, comprising the steps of:forming a first relatively harder and asecond relatively softer protruding contact on a first semiconductordevice and on least one of a second semiconductor device and a circuitboard, respectively; aligning said first protruding contact with saidsecond protruding contact; and permanently connecting said first andsecond protruding contacts together by pressing to embed at least a partof said first relatively harder protruding contact in said secondrelatively softer protruding contact.
 4. The method of claim 3, furthercomprising the step of applying an insulating material around said firstand second protruding contacts.
 5. A method for manufacturing asemiconductor device, comprising the steps of:forming a first relativelyharder and a second relatively softer protruding contact on a firstsemiconductor device and on at least one of a second semiconductordevice and a circuit board, respectively; aligning said first protrudingcontact with said second protruding contact; applying an insulatingresin around at least one of said first and second protruding contacts;permanently connecting said first and second protruding contactstogether by pressing to embed at least a part of said first relativelyharder protruding contact in said second relatively softer protrudingcontact; and hardening said insulating resin, whereby said firstsemiconductor device and said second semiconductor device or circuitboard are adhered together and said first and second protruding contactsare sealed within the hardened insulating resin thereby electricallyinsulating said protruding contacts.
 6. The method of claim 5, whereinsaid insulating resin is mixed with a reducing agent.
 7. A method formanufacturing a semiconductor device, comprising the steps of:abutting aprotruding contact formed on a first semiconductor device with asubstrate electrode of at least one of a second semiconductor device anda circuit board; applying an insulating resin comprising a reducingagent on at least one of said protruding contact and said substrateelectrode; and hardening the insulating resin.